Currently, planarite stacks up to 999 in the bag. This wouldn't be a problem, except that during some events, it's possible to get 5 full stacks of it by simply defeating the event boss. This leads to the problem of getting the "Rift bag is almost full" notice even if it were completely empty before engaging the boss, since a lot more items are also awarded.

My suggestion is to increase the stacking size to 9999.